Everyone has limbs. Your limbs are head, chest, body, left arm, right arm, left hand, right hand, left leg, right leg, left foot and right foot.
Each of these limbs has an invisible hit point total, though you can get a rough idea of how beaten up you are by typing “score”. When any of these hit point totals reaches zero, that limb is cut off, with additional effects. These invisible hit points are replenished whenever you regain hit points by eating food, and through other, usually guild-related means.
You can replace lost limbs at Genesis' Limb Shop, located four rooms south and one room west of Caladan Astroport. This is important because if you are too long without a limb, you may bleed out and die anyways. Plans are underway to make bleeding out less of an inevitability should you find yourself not on Caladan at the time.
Players under level 8 are still considered newbies and should not suffer these effects.